Process for producing white cast iron castings



Patented Dec. 14, 1948 PROCESS FOR PRODUCING, WHITE CAST moN CASTINGSOliver Small ey, Larchmont, N. Y., assignor to vMeehanite MetalCorporation No Drawing. Application September 22, 1945,. Serial No.618,059

3 Claims (01. 75-130) My invention relates to the process of the Wmanufacture of cast iron, with or without alloy ing agents, under suchcontrol asto produce white iron castings that combine both hardness andtoughness. I

By white iron, I mean a cast iron-alloy or otherwise-in which the bulkor all of the carbon is present in the form of iron carbide and whichpresents a white fracture.

White iron castings being rarely machined and selling at low competitiveprices, have not advanced technologically and industrially during thepast decade as have graycast iron castings. Generally white ironcastings are the most unpredictable products of the foundry industry andthe ideahas existed that an iron giving a white fracture is suitable forany type of hard wear service, and may be defined as white iron. Inother words, the idea has prevailed, and still prevails in certainquarters, that if an iron fractures white, then the metal'is aserviceable ma- .terial for abrasion resisting conditions and perhapsfor heat resisting purposes because it is substantially free from flakegraphite or that it can be malleablized by prolonged annealing above thecritical point.

White iron is however, not a specific material but rather a genericterm. An iron that breaks with a white fracture may be extremely brittleor it may be reasonably tough. It may present superior or inferiorresistance to abrasion. Under heat influence, it may stand'up reasonablywell or it mayfail prematurely. It "may mal1eablize in a standardannealing time and give good'combined strength and ductility, "or itsresponse to a malleablizing treatment may be quite unsatisfactory andinferior propertiesfrequently result.

White iron is commonly made-by adjusting the carbon and silicon tosuitable ratio, orit may be produced by the simple expedient of addingcar'-- usually an indeterminate material of uncertain properties. If itis to be used for abrasion resisting purposes its B. H. N.value may varyfrom 350 to 578. Its strength properties may differ as much as 100% ormore, and the casting diniculties encountered often result in rejectionof the casting because of the problemsof overcomingshrinkage defects andweakness -dependenton uncontrolled developmentof grain structure.

. Whichever method is used, the end product isi The basis of thisinvention is a process which is so controlled asto produce acasting to apredetermined degree of whiteness of known physical characteristics thathas uniform liquid shrinkage for casting purposes and is free fromcolumnar grain weakness and in which the degree of hardness and strengthproperties bear a direct relation to the sectional dimension and shapeof the finished casting.

An object of my invention is to produce a White iron to a predeterminedand controlled de-- gree of whiteness and of known physicalcharacteristics.

Another object of my invention is to produce a white iron that is freefrom crystal weakness and inherent brittleness.

Another object of my invention is to produce a white iron whosestructure is mainly equiaxed as distinct from the uncertain unbalancedcolumnar growth common to'ordinary white iron.

A further object of my invention is to produce a white iron to apredetermined abrasion resisting characteristic which is-substantiallyconstant regardless of the sectional dimensions of the finished casting,

Another object of my invention is to produce a white iron' casting freefrom shrink voids and mechanical Weakness. I

Another object of my invention is to produce ,a 'white'iron castingWhose heat resisting properwhich can be malleablized by annealing at agiven temperature and time to assure'dependable reaction tomalleablizing treatment.

A'notherobject of my invention is a two-step process for the manufactureof white iron castings, the first step comprising selecting a mixture ofraw materials which when melted Will have a structural constitutionbearing a direct relationship to thethickness of the sections to becast, and the second step comprising altering or modifying the massivecementite to produce a final structure that possesses the desiredimproved degree of toughness.

Another object of my invention is to give positive control over thephysical properties in a White iron casting, comprising the control andmeasurement of constitutional carbide values and processed carbidevalues, and regulating through'said control the relation of theconstitutional and process carbide values to each other and to thethickness of the casting to be made.

having substantially one-inch sections will be il-- casting ofsubstantially oneinch thick and of generally rectangular shape. Next, Iprocess the molten metal which, when tested, produces a processedcarbide value embraced in a range having a minimum value ofsubstantially .and a maximum value of A wedge value of (3 2) isequivalent to l-times white in a casting of substantially one inch thickand of generally rectangular shape and a wedge value of is substantiallyequivalent to 2 /z-times white. The maximum value of the constitutionalcarbide Value may not be greater than three times the maximum processcarbide value. The maximum value for the constitutional carbide would benot greater than A wedge value of /32) is substantially equivalent to 7-times white in a casting of one inch thick and of generally rectangularshape.

Corresponding proportionate wedge values would obtain for sections ofdifferent thickness. Thus, for castings of substantially 2 inches thick,the wedge values given above would be doubled, in which case, forexample, the minimum constitutional wedge value for a 2-inch sectionwould be A wedge value of 7 is substantially equivalent to I l -timeswhite in a casting of substantially 2 inches thick and of generallyrectangular shape. Other wedge values with respect to the thickness ofcastings will bear the same ratio as those set forth above for a 1-inchsection.

From the above wedge values, it is noted that the minimum constitutionalwedge value is substantially 1% times the section of a finished casting.The minimum processed wedge value is substantially 1%; times the sectionof the finished casting and the maximum processed carbide wedge value issubstantially 2% times the average section of the casting to be made.The maximum constitutional wedge value is less than 3 times the maximumvalue of the processed wedge value.

The wedge values as given above may be translated in terms of the degreeof whiteness of a casting of generally rectangular section, in whichcase the constitutional carbide value is embraced within a range havinga minimum value of 1%- times white and a maximum value as hereinafterspecified. The processed carbide values would be embraced Within a rangehaving a minimum value of l-times white to 2 /2-times white. The maximumvalue of the constitutional carbide value would be not greater than 3times the maximum processed carbide value.

Any white iron casting that is made having a constitutional carbidevalue and a processed carbide value falling within the limits of theabove defined ranges, will have good wear resisting qualities and yet betough. White iron castings made by values which lie close to the minimumvalues of the range of values will have somewhat different propertiesthan white iron castings made by values lying close to the maximumvalues of the ranges given above. A range which may represent mean.values for making white iron. castings may be as follows: Thickness ofSection yinch linch flinch Minimum Constitutional Carbide Wedge IValue"; %3 %2 %2- Maximum Constitutional Carbide Wedge Value %2 %2 %2Minimum Processed Carbide Wedge Value %2 %2 %2 Maximum Processed CarbideWedge Valuc %2 %2 962 White iron castings controlled by values lying inthe mean range given above will have a high,

heavy physical impacts.

In practicing my invention, the foundry operator first melts a charge orotherwise prepares a mixture of molten materials which, when tested, 7

gives a constitutional value lying within the range of the valueshereinabove specified with relation to the thickness of the castings tobe made. Next, the operator processes the molten material which. whentested, gives a processed carbide value lying Within the range of thevalues hereinabove specified with respect to the thickness of thecastings to be made. Having satisfied that the molten metal meets theabove requirements, the operator may now pour the processed metal in themold for making the finished white iron castings.

The foundry operator, in the practice of my invention, is able toproduce white iron castings having a controlled degree of whitenesswhereby castings made under my process have high abrasion and heatresisting characteristics which will assure long service life value. Thecastings will also have the proper characteristics, whereby they can bemalleablized by annealing at any given temperature and time and assuredependable reaction to malleablizing treatment.

Although I have described my invention in its preferred form with acertain degree of particularity, it is understood that the presentdisclosure of the preferred form has been made only by way of exampleand that numerous changes in the details of the process, modification inthe steps undertaken, variations in the materials used, and differentvalues of wedges establishing carbide balance, may be resorted towithout departing from the spirit and the scope of the invention ashereinafter claimed.

I claim as my invention:

1. A process to give positive control of the physical properties in awhite iron casting which comprises providing molten cast iron which whencast in a wedge shaped test piece and then broken in two, exhibits uponthe broken faces both gray and white iron with a line of demarcationtherebetween of such a length as to be embraced within a range having aminimum value of more than 1% times the average section to be made and amaximum value as hereinafter specified, processing the molten materialwhich when cast in a wedge shaped test piece and then broken in two,exhibits upon the broken faces a larger amount of gray iron and asmaller amount of white iron with a new and shorter line of demarcationthan that exhibited on the first men tioned test piece, said new line ofdemarcation being of such length as to be embraced within a range havinga minimum value of more than 1%; times the average section of thecasting to be made and a maximum value of less than 2% times the averagesection of the casting to be made, said a ias-p54;

maximum value of the constitutional carbide value-being not greater thanthree times the maximum process carbide value: .hereinabove specified;

.3. sALDI'OGBSS to: give positive control of the physicallpropertiesin awhite iron casting which comprises: providing molten cast iron whichproduciesca' constitutional carbide Wedge value embraced inia'rangehaving a minimum value ofat leasta substantially 2 for castings /2-,inchthick, "5 33;xi'oracastingsrsubstantially 1-inch thick and kgatorcastingssubstantially 2-inches thick and havingia maximumvalue of atleast substantially 8 for castings. substantially /g-iD-Ch' thick, V-forcastings substantially 1-inch thick,.and lfor castings substantiallyZ-inches thick, and processing the molten'materialto giveca processedcarbide wedge "value embraced within a range having a minimum value ofat least substantially 1'0r castings substantially'V -inch thick, forcastings substantially 1-inch thick, and 732 for castings substantially2-inches thick and having-a maximum'value of at leastsubstantially forcastings substantially /2-inch thick, jior castings: substantially1-inch thick, and for castings vsubstantially 2-inches thick.

GLIVER v SMALLEY.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,371,654 Smalley et a1 Mar. 20,1945 FOREIGN PATENTS Number Country Date 105,619 Australia Oct. 25, 1938

